Simple Interfaces for Complex Devices - Prof. Dr. Jeffrey Schwartz
Department of Chemistry, Princeton University
Organophosphonates have been known for decades as adhesion promoters in a variety of industrial contexts, from attaching rubber to steel belts in radial tires to enhancing adhesion of polymers to the inside of soft drink cans. Organized monolayers of phosphonates (Self‐Assembled Monolayers of Phosphonates; SAMPs) can also be of use in “high tech” devices where bulk adhesion promotion techniques are not applicable. The means to prepare such well‐defined monolayers of phosphonates on a variety of surfaces will be described in two general areas: to improve integration of tissue with synthetics; and, for control in organic electronic devices ...more
Surface treatment of synthetic materials to encourage tissue integration is a longstanding problem for the development of biomedical devices. Simple SAMP interfaces are effective for osteoblast adhesion and spreading on metals, and results from an in vivo test of one such interface are presented. Otherwise unreactive soft or hard polymers can be surface activated through the use of a nanoscale adhesion layer that is prepared by vapor phase deposition of a metal alkoxide followed by heating. This adhesion layer can then be used to attach phosphonate‐based cell adhesive or cell non‐adhesive species. In vitro tests of cell adhesion and spreading will be described for several soft and hard polymers.
The performance of simple electronic devices that use organics can be affected through manipulation of the surface chemistry of an inorganic electrode and of the interface between the organic and the electrode. For example, electroactive SAMPs can be prepared on an electrode surface to enhance hole injection in diode devices. This procedure involves formation of the SAMP of a phosphonate‐based π‐conjugated organic semiconductor on the electrode surface followed by doping with an electron acceptor. The behavior of pentacene-based organic thin‐film transistors fabricated on a silicon dioxide gate dielectric can also be affected by the introduction of SAMPs, which serve as a buffer between the SiO2 and the active pentacene channel region. Improvements in sub‐threshold slope, threshold voltage, and mobility will be described, all of which depend on the molecular structure of the SAMP; these improvements are especially significant for aromatic group‐terminated SAMPs compared to control devices. The use of a structured SAMP to affect pentacene morphology, as well as device behavior, will be described.